The present invention relates to spray guns, and more particularly to spray guns for the spraying of paint in an atomized and well controlled pattern for quality finishing of products. The spray gun is particularly adapted to paint spraying wherein paint is delivered to the gun under pressure and wherein a separate source of pressurized air is also coupled to the gun. This type of spraying is commonly refered to as air/airless paint spraying, which offers the particular advantage of providing a quality spray finish under nominal paint and air pressure conditions.
In the art of paint spraying it has long been known that quality spray finishes can be obtained by the controlled application of pressurized air to both atomize the paint and control the direction and shaping of the atomized pattern of paint. Likewise, it has been known that spray finishing can be accomplished by hydraulically pressurizing the paint to high pressures, in the order of 1,000-3,000 pounds per square inch (PSI), and ejecting this pressurized paint through a very small spray orifice for atomization. In all cases, such spray guns have commonly utilized trigger mechanisms mechanically coupled to valves for unseating the valve and releasing air or paint for spraying. In some cases, high pressure paint valves have been operable through the use of an air assist piston, whereby a source of pressurized air is coupled to the gun for the primary purpose of actuating a miniature air piston/cylinder to assist in unseating a liquid flow valve and thereby require less finger pressure to actuate the trigger. Air assist valves have typically been utilized in spray guns where high hydraulic pressures have been developed for spraying in the paint, for such paint control valves require unusually large spring forces for seating the valves to prevent leakage. These seating forces must be overcome when the valve is opened and air cylinders have been found useful for this purpose.
In a paint spray gun utilized for air/airless paint spraying there is a need for the proper control of two valves. One of these valves is a paint liquid sealing valve and the other valve is an air release valve to permit the proper and timely introduction of pressurized air to the painting process. It has been found preferable, when actuating air/airless spray guns, to first release the pressurized air, slightly ahead of the release of pressurized paint at the time the spray operation is started. Likewise, when spray operation is finished it is preferable to first disconnect the flow of pressurized paint and second disconnect the pressurized air supply. This procedure for opening and closing the respective valves has been found to provide the best overall spray painting operation under air/airless painting conditions.